Biasing correction for simple GMR head

ABSTRACT

An spin valve sensor is provided with a ferromagnetic free layer, a ferromagnetic pinned layer, and a nonferromagnetic spacer layer separating the free layer and the pinned layer. The magneto resistance of the spin valve sensor is increased by increasing the thickness of the pinned layer. To counter a magnetic field induced in the free layer by the thicker pinned layer, a biasing layer is used. The bias layer helps achieve a desired orientation of the magnetic fields of the free layer and the pinned layer to be offset by 90 degrees in the absence of an external magnetic field. The bias layer is located to a side of the pinned layer opposite the free layer. The bias layer is selected to be magnetically soft and to have a high resistivity and may be formed of CoFe or CoHfNbFe. The thickness of the bias layer is selected to be approximately equivalent to the increase in thickness of the free layer from a previously biased amount.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

This invention relates generally to spin valve magnetic transducers forreading information signals from a magnetic medium and, in particular,to increasing the thickness of a pinned layer for a spin valve sensor,and to magnetic recording systems which incorporate such sensors.

2. The Relevant Technology

Computer systems generally utilize auxiliary memory storage deviceshaving media on which data can be written and from which data can beread for later use. A direct access storage device (disk drive)incorporating rotating magnetic disks is commonly used for storing datain magnetic form on the disk surfaces. Data is recorded on concentric,radially spaced tracks on the disk surfaces. Magnetic heads includingread sensors are then used to read data from the tracks on the disksurfaces.

In high capacity disk drives, magnetoresistive read sensors, commonlyreferred to as MR heads, are the prevailing read sensors because oftheir capability to read data from a surface of a disk at greater lineardensities than thin film inductive heads. An MR sensor detects amagnetic field through the change in the resistance of its MR sensinglayer (also referred to as an “MR element”) as a function of thestrength and direction of the magnetic flux being sensed by the MRlayer.

The conventional MR sensor operates on the basis of the anisotropicmagnetoresistive (AMR) effect in which an MR element resistance variesas the square of the cosine of the angle between the magnetization ofthe MR element and the direction of sense current flowing through the MRelement. Recorded data can be read from a magnetic medium because theexternal magnetic field from the recorded magnetic medium (the signalfield) causes a change in the direction of magnetization in the MRelement, which in turn causes a change in resistance in the MR elementand a corresponding change in the sensed current or voltage.

Another type of MR sensor, more recently developed, is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, theresistance of the MR sensing layer varies as a function of thespin-dependent transmission of the conduction electrons between magneticlayers separated by a non-magnetic layer (spacer) and the accompanyingspin-dependent scattering which takes place at the interface of themagnetic and non-magnetic layers and within the magnetic layers.

GMR sensors using two layers of ferromagnetic material separated by alayer of non-magnetic electrically conductive material are generallyreferred to as spin valve (SV) sensors manifesting the GMR effect. In anSV sensor, one of the ferromagnetic layers, referred to as the pinnedlayer, has its magnetization typically pinned by exchange coupling withan antiferromagnetic (e.g., NiO or Fe—Mn) layer.

The magnetization of the other ferromagnetic layer, referred to as thefrce layer, however, is not fixed and is free to rotate in response tothe field from the recorded magnetic medium (the signal field). In SVsensors, the SV effect varies as the cosine of the angle between themagnetization of the pinned layer and the magnetization of the freelayer. Recorded data can be read from a magnetic medium because theexternal magnetic field from the recorded magnetic medium causes achange in the direction of magnetization in the free layer, which inturn causes a change in resistance of the SV sensor and a correspondingchange in the sensed current or voltage.

FIG. 1 shows a simple SV sensor 100 comprising a pair of end regions 104separated by a central region 102. The central region 102 is formed by asuitable method such as sputtering onto a substrate 105 and has definedend regions that are contiguous with and abut the edges of the centralregion. A free layer (free ferromagnetic layer) 110 is separated from apinned layer (pinned ferromagnetic layer) 120 by a non-magnetic,electrically-conducting spacer 112. The magnetization of the pinnedlayer 114 is fixed through exchange coupling with an anti ferromagnetic(AFM) layer 116.

A seed layer 109, the free layer 110, a spacer 112 the pinned layer 114,the AFM layer 116, and the cap layer 118 are all formed in the centralregion 102. Hard bias layers 120, formed in the end regions 104, providelongitudinal bias for the free layer 110. Leads 122 formed over the hardbias layers 120 provide electrical connections for the flow of thesensing current I_(S) from a current source 124 to the MR sensor 100. Asensing device 126 connected to the leads 122 senses the change in theresistance of the free layer 110 and the pinned layer 114 due to changesinduced by an external magnetic field such as the field generated by adata bit stored on a disk drive media. IBM's U.S. Pat. No. 5,206,590granted to Dieny et al. and incorporated herein by reference, disclosesa GMR sensor operating on the basis of the SV effect.

One key to proper operation of a spin valve sensor is properly biasingthe magnetization of the free layer so that the magnetization of thepinned and free layers are oriented in the manner shown in FIG. 1 FIG. 2shows the simple GMR spin valve sensor 100 of FIG. 1 rotated 90 degrees.The spin valve sensor 100 of FIG. 2 is shown with the air bearingsurface at the bottom of the drawing (not shown). Seen in FIG. 2 arevarious magnetic fields of a properly biased spin valve sensor 100. Thecurrent I_(S) passing through the sensor 100 is directed between theleads 106 (not shown) in a direction 125 coming out of the page. Themagnetization M_(P) from the pinned layer 114 is pinned through exchangecoupling with the AFM in a direction 128 pointing down in the free layer110.

The magnetization M_(P) of the pinned layer 114 induces a demagnetizingfield H_(D) through the free layer 110 with an orientation 132 pointingup. A field Hc also results from magnetic coupling between the pinnedlayer 114 and the free layer 110. The magnetic coupling field Hc has adirection 134 going down in FIG. 2. A field His is induced within thefree layer 110 as a result of the current I_(S) and has a direction 130acting downward through the free layer. As a result of the biasingthrough the cumulation of the fields in the sensor (including biasingfrom the hard bias layers 120), the free layer 110 has a resultantmagnetization M_(F) oriented with a direction 130 acting perpendicularto the direction 128 of the magnetization M_(P) of the pinned layer 114.Preferably, the magnetization M_(F) has a direction pointing either intoor out of the page. In the depicted sensor 100, the magnetization M_(F)has a direction 130 pointing out of the page.

In this arrangement, where the magnetization M_(F) in the free layer 110and the magnetization M_(P) in the pinned layer 114 are perpendicular toeach other, the external magnetic field from the magnetized bits of thedisk drive cause the magnetization M_(F) to rotate (or “spin”) to adirection pointing either up or down depending on the value of thestored bit. For instance, an external magnetic field indicating a zeromay have a direction causing the magnetization M_(F) to rotate down to adirection parallel to the magnetization Mp, resulting in a lowresistance condition in the sensor 100. An external magnetic fieldindicating a one may have a direction causing the magnetization Mp torotate up to a position antiparallel to the magnetization Mp, resultingin a high resistance condition in the sensor 100.

When the magnetizations M_(P) and M_(F) are parallel, less electrons arescattered (ostensibly because only electrons with a spin in onedirection are affected by the fields) and when the magnetizations M_(P)and M_(F) are antiparallel, more electrons are scattered (becauseelectrons of both spin types are affected), causing a higher resistancecondition. By monitoring these high and low resistance conditions, theapplied external magnetic fields representing ones and zeroes on thedisk drive media can be properly detected by the sensing device 126 evenat the higher densities becoming more common in current disk drives. onany given disk surface. In so doing, it has been found that increasingthe thickness of the pinned layer can lead to an increase in themagnetoresistance (dR/R) of the sensor. A thicker pinned layer causes areduction in boundary scattering, which in turn results in greatermagnetoresistance of the sensor.

Nevertheless, increasing the thickness of the pinned layer has beenfound to increase the demagnetizing field H_(D) and consequently alterthe bias of the aforementioned magnetic fields within the free layer.This altered bias in turn causes a negative asymmetry of the readsignal. Symmetry of the read signal of the spin valve sensor isdetermined by the orientation of the magnetic fields His andmagnetizations Mp of the free and pinned layers. When the pinned layeris increased in prior art spin valve sensors, the signal asymmetryincreases such that the sensing device 126 cannot properly detect thechanges in resistance.

One manner in which the prior art has attempted to correct the bias of aspin valve sensor when increasing the thickness of the pinned layer iswith the use of a keeper layer. Referring to FIG. 3, shown therein is apartial cross-sectional view of a prior art simple spin valve sensor 150having a keeper layer 152 of the prior art. The spin valve sensor 150 isconfigured substantially in the same manner as the spin valve sensor 100of FIGS. 1 and 2, with the exception of the added keeper layer 152 and aspacer layer 154.

The keeper layer, when thicker than the pinned layer, produces ademagnetization field Hk in the free layer that partially opposes theincreased demagnetizing field H_(D) from thicker pinned layer. Theresult is a more properly biased simple spin valve sensor with a thickerpinned layer. The increase in the thickness of the keeper layer 152 tocreate the proper bias must be substantially in excess of the increasein the thickness of the pinned layer. A thick keeper layer isproblematic because it results in a high amount of shunting of thecurrent I_(S) through the keeper layer 152. This current shuntingreduces the current flowing through the pinned and free layers andconsequently reduces the magnetoresistance of the sensor.

Thus, it can be seen from the above discussion that there is a needexisting in the art for an improved spin valve sensor with an increasedmagnetoresistance. Particularly, it would be advantageous to provide aspin valve sensor achieving an increased magnetoresistance throughincreasing the thickness of the pinned layer, while maintaining a properbiasing without a corresponding increase of current shunting.

OBJECTS AND BRIEF SUMMARY OF THE INVENTION

The apparatus of the present invention has been developed in response tothe present state of the art, and in particular, in response to theproblems and needs in the art that have not yet been fully solved bycurrently available spin valve sensors. Thus, it is an overall objectiveof the present invention to provide an improved spin valve sensor withan increased magnetoresistance through an increased pinned layerthickness.

To achieve the foregoing object, and in accordance with the invention asembodied and broadly described herein in the preferred embodiments, aspin valve sensor with a thicker pinned layer is provided. The spinvalve sensor maintains a proper bias of the magnetization in the freelayer through the use of a bias layer disposed to a side of the pinnedlayer opposite the free layer.

The spin valve sensor of the present invention in one embodimentcomprises a free layer formed of a first ferromagnetic material; apinned layer formed of a second ferromagnetic material; a spacer layerinterposed between the free layer and the pinned layer, the spacer layerformed of a nonferromagnetic conducting material; and a bias layerlocated to a side of the pinned layer opposite the free layer, the biaslayer configured to at least partially bias the magnetization of thefree layer.

The spin valve sensor may also comprise an AFM layer exchange coupledwith the pinned layer. The AFM layer is preferably disposed to a side ofthe pinned layer opposite the free layer. The spin valve sensor may alsocomprise a substrate. Preferably, the free layer, the pinned layer, thespacer layer, and the bias layer are formed on the substrate. A caplayer is preferably formed atop the stack of the aforementioned layers.

In one embodiment, the AFM layer is located adjacent to the pinnedlayer, and a spacer layer is interposed between the AFM layer and thebias layer. The spacer layer is preferably formed substantially oftantalum. The pinned layer is preferably formed of a Co and Fe alloy.

The bias layer may comprise a Co and Fe alloy, and the Co and Fe alloymay also comprise Hf and Nb. In one embodiment, the bias layer has athickness substantially equivalent to the thickness of the free layerabove 25 angstroms. The bias layer may have a thickness in a range ofbetween about 10 and about 30 Angstroms. In a preferred embodiment, thebias layer has a thickness of about 25 Angstroms.

In one embodiment, the pinned layer has a thickness in a range ofbetween about 40 and 50 Angstroms and the bias layer has a thickness ina range of about between about 15 and 25 Angstroms. The AFM layer may beformed of a material selected from a group consisting of PtMn, IrMn, andNiMn. The pinned layer may be formed with a thickness in a range ofbetween about 30 and about 60 Angstroms. Alternatively, the pinned layermay be formed with a thickness in a range of between about 40 and about50 angstroms.

The bias layer is preferably situated to produce a magnetic field as aresult of a current applied to the spin valve sensor. The magnetic fieldof the bias layer preferably opposes and partially cancels ademagnetizing field created within the free layer by the magnetizationof the pinned layer. Preferably, the magnetic field of the bias layer isoriented in a direction causing the magnetization of the free layer tobe oriented in a direction substantially perpendicular to an orientationof a magnetization of the pinned layer in the absence of an appliedexternal magnetic field. Thus, the pinned layer is preferably formedwith a thickness greater than about 30 angstroms while the magnetizationwithin the free layer exhibit substantially no asymmetry.

The spin valve sensor of the present invention may be incorporatedwithin a disk drive system comprising a magnetic recording disk; a spinvalve (SV) sensor configured in the manner discussed above; an actuatorfor moving said spin valve sensor across the magnetic recording disk sothe spin valve sensor may access different regions of magneticallyrecorded data on the magnetic disk drive media; and a detectorelectrically coupled to the spin valve sensor for detecting changes inresistance of the sensor caused by rotation of the magnetization axis ofthe free ferromagnetic layer relative to the fixed magnetizations of theAP-pinned layer in response to magnetic fields from the magneticallyrecorded data.

These and other objects, features, and advantages of the presentinvention will become more fully apparent from the following descriptionand appended claims, or may be learned by the practice of the inventionas set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained will be readily understood, amore particular description of the invention briefly described abovewill be rendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 is a cross-sectional view illustrating the composition of a spinvalve sensor of the prior art;

FIG. 2 is a cross-sectional view illustrating the spin valve sensor ofFIG. 1 with the view rotated 90 degrees;

FIG. 3 is a cross-sectional view illustrating the composition of a spinvalve sensor of the prior art incorporating a keeper layer.

FIG. 4 is a schematic block diagram illustrating one embodiment of amagnetic recording disk drive system of the present invention;

FIG. 5 is a cross-sectional view illustrating the composition of oneembodiment of a spin valve sensor of the present invention.

FIG. 6 is a cross-sectional view illustrating the spin valve sensor ofFIG. 5 with the view rotated 90 degrees.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 4 shows one example of a disk drive 300 embodying the presentinvention. As shown in FIG. 4, the disk drive 300 comprises at least onerotatable magnetic disk 312 supported on a spindle 314 and rotated by adisk drive motor 318. The magnetic recording media on each magnetic disk312 is in the form of an annular pattern of concentric data tracks (notshown).

At least one slider 313 is positioned on the disk 312. Each slider 313supports one or more magnetic read/write heads 321 incorporating the GMRsensor of the present invention. As the disks rotate, the slider 313 ismoved radially in and out over the disk surface 322 so that the heads321 may access different portions of the magnetic disk 312 where desireddata is recorded. Each slider 313 is attached to an actuator arm 319 bymeans of a suspension 315. The suspension 315 provides a slight springforce which biases the slider 313 against the disk surface 322. Eachactuator arm 319 is attached to an actuator means 327.

The actuator means as shown in FIG. 4 may be a voice coil motor (VCM).The VCM comprises a coil movable within a fixed magnetic field, thedirection and speed of the coil movements being controlled by the motorcurrent signals supplied by a controller 329.

During operation of the disk storage system, the rotation of themagnetic disk 312 generates an air bearing between the slider 313 (thesurface of slider 313 which includes the head 321 and faces the surfaceof disk 312 is referred to as an air bearing surface (ABS)) and the disksurface 322 which exerts an upward force or lift on the slider 313. Theair bearing thus counter-balances the slight spring force of thesuspension 315 and supports the slider 313 off and slightly above thedisk surface by a small, substantially constant spacing duringoperation.

The various components of the disk storage system are controlled inoperation by control signals generated by the control unit 329, such asaccess control signals and internal clock signals. Typically, thecontrol unit 329 comprises logic control circuits, storage means and amicroprocessor. The control unit 329 generates control signals tocontrol various system operations such as drive motor control signals ona line 323 and head position and seek control signals on a line 328. Thecontrol signals on the line 328 provide the desired current profiles tooptimally move and position the slider 313 to the desired data track onthe disk 312. Read and write signals are communicated to and from theread/write heads 321 by means of a recording channel 325. In thedepicted embodiment, the read/write heads 321 incorporate a GMR sensorincluding a spin valve of the present invention.

FIGS. 5 and 6 depict the composition of one embodiment of a preferredspin valve 400 of the present invention including a thicker pinned layerand a bias layer. FIG. 5 shows an air bearing surface (ABS) view of theSV sensor 400 according to one embodiment of the present invention.While a top GMR structure with the AFM on top of the stack of layers isdepicted, a bottom GMR structure with the AFM on bottom of the stackcould also be used with the present invention.

The spin valve sensor 400 of FIG. 5 is shown with a pair of end regions402 separated from each other by a central region 404. The centralregion 404 has defined edges where the end regions 402 form a contiguousjunction with and abut said edges. The sensor 400 is built upon asubstrate 406, which may be any suitable substance, including glass,semiconductor material, or a ceramic material, such as alumina (Al₂O₃).

The spin valve sensor 400 may also comprise a shield layer 408 and a gaplayer 410 as is known to those skilled in the art. A seed layer 412 maybe provided to help orient the crystalline structure grown above it.Shown above the seed layer 412 is a free layer 414. The free layer 414is preferably formed of a material having a high magnetoresistance suchas Co of CoFe. Above the free layer 414 is shown a spacer layer 416. Inone embodiment, the spacer layer 416 is formed of a conducting,nonferromagnetic material such as copper.

A pinned layer418 is formed above the spacer layer. Preferably, thepinned layer 418 is formed of a magnetoresistive material such as Co orCoFe. An antiferromagnetic (AFM) layer 420 is formed over the pinnedlayer 418 in the central region 404. The AFM layer 420 is, in oneembodiment, formed of PtMn, although it may also be formed of othertypes of antiferromagnetic material such as a Mn alloys, including NiMn.The pinned layer 418 pins the direction 436 of magnetization of thepinned layer 418 through exchange coupling. In the depicted embodiment,the magnetization of the pinned layer 418 is pinned in a directioncoming out of the page.

In accordance with the present invention, in order to allow theformation of a thicker pinned layer 418, a bias layer 422 and a spacerlayer 425 are formed on a side of the pinned layer opposite the freelayer 414. In the depicted embodiment, the spacer layer 425 is formedabove the AFM layer 420, and the bias layer 422 is formed above thespacer layer 425.

In one embodiment, the spacer layer 425 is formed of Ta and the biaslayer 422 is formed of a material such as CoFe or CoHfNbFe. The spacerlayer 425 is preferably formed with a thickness of about 20 Angstroms.The bias layer 422 is preferably formed with a thickness selected tocounter the increased demagnetization field of thicker pinned layer.Thus, the bias layer 422 preferably causes a biasing of themagnetization of the free layer 414 such that the free layer 414 has amagnetization with a direction 434 parallel to the ABS. Alternatively,the direction 434 could be directed to the left. Typically, the biaslayer 422 is selected to have a thickness corresponding to an increasedthickness of the pinned layer 418 in excess of a previously biasedthickness.

As an example, current pinned layers 418 are currently thought to beproperly biasable when having a thickness of about 25 Angstroms. If thethickness of the pinned layer is increased from this properly biasablethickness to a thickness of, for instance, 40 Angstroms, the bias layer422 is selected to have a thickness of about 15 Angstroms.

Currently, it is preferred to increase the thickness of the pinned layerto a thickness in a range of between about 30 to 50 Angstroms. Atthicknesses in excess of 50 Angstroms, excess current shunting throughthe pinned layer occurs. A more preferred thickness is in a range ofbetween about 40 to 45 Angstroms, and a thickness of about 45 Angstromsis currently most preferred. Thus, for the preferred pinned layerthickness of 45 Angstroms, the bias layer may have a thickness of about20 Angstroms. Of course, thicknesses may vary according to theparticular configuration of the other layers, but the principle ofincreasing the thickness of the bias layer 422 concurrently withincreasing the thickness of the pinned layer 418 in order to properlybias the magnetization in the free layer 414 is a constant overridingfactor of the present invention.

A pair of electrical leads 428 are also shown formed over the biasinglayers 426 and are employed to form a circuit path between the spinvalve sensor 400 and a current source 430 and a sensing device 432. Inthe preferred embodiment, magnetic signals in the recorded medium (e.g.,the disk 312 of FIG. 4) are sensed by the sensing device 432 in the formof a voltage differential (voltage signal) between the two leads 428.

The sensed voltage signal arises from a change in resistance, ΔR, of thecentral portion 404 as the direction of the magnetic field H_(IS) of thefree layer 420 rotates in response to the applied external magneticsignal from the recorded medium. The sensing device 432 may include adigital recording channel such as a partial-response maximum likelihood(PRML) channel as is known to those skilled in the art. Alternatively,it may include a peakdetect channel as is known to those skilled in theart. In the preferred embodiment of the present invention, the sensingdevice includes a digital recording channel of the type known in the artas partial-response maximum-likelihood.

FIG. 6 shows the sensor 400 of FIG. 5 rotated 90 degrees such that theABS is at the bottom of the page, and the view looks through the bardbias layers 426. FIG. 6 shows a magnetization M_(B) induced within thebias layer 422 in a direction 446 pointing up. The magnetization M_(B)is directly induced by the current I_(S), which flows through the sensor400 in the direction 440 shown as coming out of the page. The flux ofthe magnetic field H_(D) returns through the free layer 414 in adirection 448 shown pointing down. The downward pointing magnetic fieldH_(B) offsets the increased demagnetizing field H_(D) generated by theincreased-thickness pinned layer 418. Thus, the offsetting bias layerfield H_(B) results in a cumulative magnetization M_(F) in the freelayer with a direction 438 perpendicular to the ABS (shown directed outof the page in FIG. 6).

A symmetrical configuration results, with the directions of themagnetization of the free layer 414 and the pinned layer 418perpendicular to each other. Thus, when the applied magnetic signal fromthe recording medium is encountered, the swing of the magnetizationM_(F) is substantially equal in each direction, resulting in a desiredsymmetry.

From the above-discussion, it should be readily apparent that theimproved free layer of the present invention provides the advantages ofincreased magnetoresistance through a thicker pinned layer whilemaintaining a proper bias of hte magnetic fields within the free layerand without excess current shunting.

The present invention may be embodied in other specific forms withoutdeparting from its essential characteristics. The described embodimentsare to be considered in all respects only as illustrative and notrestrictive. The scope of the invention is, therefore, indicated by theappended claims rather than by the foregoing description. All changeswhich come within the meaning and range of equivalency of the claims areto be embraced within their scope.

What is claimed is:
 1. A spin valve sensor, comprising: a free layerformed of a first ferromagnetic material; a pinned layer formed of asecond ferromagnetic material; a spacer layer interposed between thefree layer and the pinned layer, the spacer layer formed of anonferromagnetic conducting material; and a bias layer located to a sideof the pinned layer opposite the free layer, the bias layer comprising aCo, Fe, Hf, and Nb alloy configured to at least partially bias themagnetization of the free layer.
 2. The spin valve sensor of claim 1,further comprising an AFM layer exchange coupled with the pinned layer.3. The spin valve sensor of claim 2, wherein the AFM layer is locatedadjacent to the pinned layer, and further comprising a spacer layerinterposed between the AFM layer and the bias layer.
 4. The spin valvesensor of claim 3, wherein the spacer layer is formed substantially oftantalum.
 5. The spin valve sensor of claim 1, further comprising asubstrate, the free layer, pinned layer, spacer layer, and bias layerformed on the substrate, and a cap layer disposed adjacent the biaslayer, opposite the substrate.
 6. The spin valve sensor of claim 1,wherein the bias layer has a thickness substantially equivalent to thethickness of the free layer in excess of 25 angstroms.
 7. The spin valvesensor of claim 1, wherein the bias layer has a thickness in a range ofbetween about 10 and about 30 Angstroms.
 8. The spin valve sensor ofclaim 1, wherein the bias layer has a thickness of about 25 Angstroms.9. The spin valve sensor of claim 1, wherein the pinned layer has athickness in a range of between about 40 and 50 Angstroms and the biaslayer has a thickness in a range of about between about 15 and 25Angstroms.
 10. The spin valve sensor of claim 1, wherein the AFM layeris formed of a material selected from the group consisting of PtMn,IrMn, and NiMn.
 11. The spin valve sensor of claim 1, wherein the pinnedlayer is formed with a thickness in a range of between about 30 and 60Angstroms.
 12. The spin valve sensor of claim 1, wherein the pinnedlayer is formed with a thickness in a range of between about 40 andabout 50 angstroms.
 13. The spin valve sensor of claim 1, wherein thepinned layer is formed from a Co and Fe alloy.
 14. The spin valve sensorof claim 1, wherein the bias layer is situated to produce a magneticfield as a result of a current applied to the spin valve sensor, themagnetic field of the bias layer opposing and partially canceling ademagnetizing field created within the free layer by the magnetizationof the pinned layer.
 15. The spin valve sensor of claim 14, wherein themagnetic field of the bias layer is oriented in a direction causing themagnetic field of the free layer to be oriented in a directionsubstantially perpendicular to an orientation of a magnetic field of thepinned layer in the absence of an applied external magnetic field. 16.The spin valve sensor of claim 1, wherein the pinned layer is formedwith a thickness greater than about 30 angstroms and the magnetic fieldwithin the free layer exhibits substantial symmetry.
 17. A disk drivesystem, comprising: a magnetic recording disk; a spin valve sensor forreading data recorded on the recording disk, comprising: a free layerformed of a first ferromagnetic material; a pinned layer formed of asecond ferromagnetic material; a spacer layer interposed between thefree layer and the pinned layer, the spacer layer formed of anonferromagnetic conducting material; and a bias layer located to a sideof the pinned layer opposite the free layer, the bias layer comprising aCo, Fe, Hf, and Nb alloy configured to at least partially bias themagnetization of the free layer; an actuator for moving said spin valvesensor across the magnetic recording disk so the spin valve sensor mayaccess different regions of magnetically recorded data on the magneticrecording disk; and a detector electrically coupled to the spin valvesensor for detecting changes in resistance of the sensor caused byrotation of the magnetization axis of the free ferromagnetic layerrelative to the fixed magnetizations of the pinned layer in response tomagnetic fields from the magnetically recorded data.
 18. The disk drivesystem of claim 17, wherein the bias layer is situated to produce amagnetic field as a result of a current applied to the spin valvesensor, the magnetic field of the bias layer opposing and partiallycanceling a demagnetization field created within the free layer by themagnetization of the pinned layer.
 19. The disk drive system of claim17, wherein the magnetization field of the bias layer is oriented in adirection causing the magnetization of the free layer to have adirection substantially perpendicular to a direction of a magnetizationof the pinned layer in the absence of an applied external field.